This invention relates to an improved high pressure fuel injection unit for engines and more particularly to an improved accumulator type fuel injection nozzle that will provide the desired degree of fuel discharge with a simple valving and control arrangement.
There is a very popular type of fuel injection system that employs an accumulator type of fuel injection nozzle. With this type of system, fuel is delivered under pressure to an accumulator chamber and a flow controlling injection valve is slidably supported in that chamber and controls the flow from the chamber to the engine through a nozzle port. An actuating member is slidably supported within a smaller control chamber and is associated with the fuel controlling injection valve for effecting opening of the injection valve and closing of it. The control chamber is charged with fuel under pressure from the injection system, normally from the accumulator chamber, and a relief valve selectively dumps the pressure in the control chamber. The pressure differences acting on the actuating member then cause the injection valve to open and discharge fuel. This type of injection nozzle is, as noted, very popular and highly effective.
In conjunction with certain types of engine applications, for example, diesel engines, it is known that it is extremely important to control the timing and amount of fuel injection during the injection cycle. It has been found that it is desirable to provide a low initial amount of fuel injection when the injector valve first opens and then an increasing amount of fuel flow is desired. This type of arrangement is effective in controlling the operation of the diesel engine and particularly so as to insure favorable exhaust gas conditions. That is, the emission control of a diesel engine is particularly dependent upon the timing of the fuel injection.
Most accumulator type injection nozzles of the type described, however, do not lend themselves to tailoring of the flow to varying rates during the injection cycle. A wide variety of arrangements have been incorporated for attempting to provide a lesser than normal amount of fuel discharge during the initial fuel valve opening. One way this can be done is by supplying a pair of control valves that operate to control the pressure in the accumulator chamber, each of which is operated by a separate electromagnet. Although such devices can be practical, they become quite complicated and expensive. In addition, the additional circuitry required makes the injector nozzle quite complicated.
It is, therefore, a principal object of this invention to provide an improved high pressure fuel injection unit for an engine.
It is a further object of this invention to provide an improved high pressure accumulator type injection nozzle in which the amount of initial fuel discharge can be restricted from conventional systems through a very simple and highly effective manner.
It is a further object of this invention to provide an improved injector nozzle of the accumulator type wherein a biasing spring arrangement is incorporated that is tailored so as to insure that the proper rates and timing of fuel injection can be achieved without requiring additional control valves and valving elements.